1. Field of the Invention
The present invention relates to a water base pigment ink for ink-jet recording which is excellent in the drying performance on the paper surface and which makes it possible to avoid the occurrence of the feathering and the blank stripes in letters, an ink cartridge which accommodates the same, and an ink-jet recording method.
2. Description of the Related Art
In the ink-jet recording system, ink droplets are formed by the ink discharge system including, for example, the electrostatic attraction system, the system in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element, and the system in which bubbles are generated by heating the ink to utilize the pressure generated thereby. All or a part of the ink droplets are adhered to a recording objective material such as paper to perform the recording.
Those used as the ink for ink-jet recording employed for the ink-jet recording system as described above include those in which various water-soluble dyes or pigments are dissolved or dispersed in liquid media composed of water and other components. For example, it is required for the ink for ink-jet recording that neither precipitation nor coagulation is caused even when the ink is not used for a long period of time, the ink is not clogged up in the ink flow passage and at the tip of the head of the ink-jet printer, the printing quality is satisfactory, and the weather resistance is excellent.
The dye and the pigment are compared with each other as follows. The dye is unsatisfactory in the water resistance, because the dye is completely dissolved in the ink medium composed of water and the like. The dye is fairly inferior in the weather resistance in view of the chemical structure thereof. On the contrary, the pigment is extremely satisfactory in the weather resistance including the water resistance, because the pigment is not dissolved but dispersed in the ink medium. In particular, the pigment ink is easily solidified after the evaporation of water. Once the pigment ink is solidified on the paper surface, the strong bond is formed between the pigment and the paper. Therefore, the pigment ink is more excellent in the securing performance on the paper than the dye ink. This function is further facilitated when the resin is contained as the dispersing agent or the binder in the pigment ink. Therefore, in recent years, the ink for ink-jet recording is being shifted from the dye ink to the pigment ink.
In recent years, it is demanded to use a pigment ink for ink-jet recording having a printing quality equivalent to that of a photographic image in which the contour of an image after the printing is sharp, and the blurring such as feathering and bleeding is suppressed as extremely as possible. For the purpose of realizing the printing quality as described above, the pigment ink for the ink-jet printer is added with a water-soluble organic solvent called “permeating agent” in order to quickly permeate the ink into the printing paper and solve the problems of the feathering and the drying performance on the paper surface. Those known as the permeating agent include, for example, glycol-based n-butyl ethers such as diethylene glycol-n-butyl ether, triethylene glycol-n-butyl ether, propylene glycol-n-butyl ether, dipropylene glycol-n-butyl ether, and tripropylene glycol-n-butyl ether. For example, Japanese Patent Application Laid-open No. 8-283631 discloses an ink for ink-jet recording containing, for example, propylene glycol mono butyl ether and dipropylene glycol mono butyl ether. The feathering refers to such a phenomenon that the ink is permeated along paper fibers existing irregularly which results in a shaggy and indistinct image when the printing is performed, for example, on the regular paper having the surface which is not subjected to the coating.
However, the permeating agent, which has been hitherto used, has the too large permeability into the paper. Therefore, in order to realize the printing quality approximately equivalent to that of the laser printer in which the feathering is caused extremely scarcely, it is necessary that the permeability into the paper is suppressed by decreasing the amount of addition of the permeating agent. If the amount of addition of the permeating agent is decreased, a problem has arisen such that the drying performance on the paper surface is deteriorated, and it is impossible to obtain any sufficient paper surface drying performance. Further, if the amount of addition of the permeating agent is decreased, the permeability into the paper is lowered. For this reason, a problem has arisen such that blank or white stripes in letter portions appear after the printing. Therefore, an ink has been demanded, in which the feathering and the blank stripes in letters do not occur while securing the excellent paper surface drying performance.